Typically in an extrusion and injection molding machine, a screw is positioned in a barrel to mix and convey resinous material from an inlet feed at one end of the barrel to an outlet discharged point at a distal end of the barrel. A typical configuration of the screw within the barrel includes a feed section at the inlet end, a transition section, and a metering section at the discharge end. The feed section of the screw conveys the resin forward in the barrel by the rotation of the screw. The resin is partially melted in this section. The resin then moves into the transition section wherein the diameter of the root of the screw gradually increases to compress and further heat the resin. The final section is the metering section which includes a constant large root diameter to completely melt the material. The screw further includes a helical thread (or flights) to mix and transport the resin forward through the barrel as the screw rotates.
Because the barrel is heated, various configurations for the screw have been offered to provide complete mixing of the material while preventing overheating. Some screw designs alter the transition section such that a secondary flight or protuberances are formed to interrupt the continuous path of the resin material such that mixing and melting of the material is further promoted.
Although the prior art has provided effective screws, it is desirable to provide additional improvements. A consideration for an improved screw design is one that does not allow the resin material to hang up on sharp corners or edges so that flow is not blocked. Another consideration includes providing a free flow path for the resin in the metering section where the root diameter is large to prevent burning of the material. A further consideration is to design a screw that allows a wider range of materials that can employ the injection and extruder machine, especially heat sensitive materials with high viscosity.